The deltaic succession of the Campanian Chimney Rock Tongue exhibits high-frequency alternation of wave- and river-dominated delta fronts. The deltaic succession is exposed in a dip-oriented, ca 15 km long outcrop belt in the Flaming Gorge area, Utah/Wyoming. The delta succession consists of eastward-prograding clinothem sets. River-dominated delta fronts are recognized as upward-coarsening packages of turbidites, slumped beds and mouth-bar deposits. The wave-dominated delta fronts consist of offshore transition to shoreface deposits. The river-dominated clinothems tend to have a higher degree of internal heterogeneity. In addition, the river-dominated clinothems are steeper (2-4°), and shorter (200-400m) than wave-dominated clinothems (800-1200m long, dip at 0.1-0.3°). Tops of both types of clinothems are locally cut by distributary channels, filled with fluvial and tide-influenced fluvial deposits. The wave- and river-dominated clinothem sets display the following alternation styles within individual clinothem sets (parasequences): (1) river-dominated delta toes are sharply overlain by a wave-dominated delta front; (2) a river-dominated delta front is seaward sharply replaced by a wave-dominated delta front; (3) a wave-dominated delta front is seaward replaced by a river-dominated delta front; and (4) wave-dominated delta toes are overlain by a river-dominated delta front. These sub-parasequence scale alternations indicate that autogenic rather than allogenic processes, like relative sea-level changes, hinterland tectonics or major climate changes control the alternations. The alternation styles indicate that older river-dominated delta-front packages are partially reworked by wave processes, and river-dominated delta fronts may be replaced seaward by wave-dominated delta fronts or vice versa. These lateral and vertical relationships suggest that the river-dominated delta fronts are associated with active distributary channel mouths. After a distributary channel gets abandoned, the river-dominated delta fronts are partially or completely reworked by waves. This interpretation is supported by high feldspar content in the wave-dominated deposits, indicating a local sediment source rather than far-range long-shore transport. Recognizing this river- and wave-dominated delta front alternation across lateral distances of a few kilometers, and vertical thicknesses of a few to a few tens of meters, alerts for caution for correlations across large distances.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009